Fourth-seeded Li stormed to a 6-1, 6-4 win against Russia's Anastasia Pavlyuchenkova while seventh seed Bartoli, who won her first Grand Slam title at Wimbledon last month, took the first seven games of her match with America's Lauren Davis in a 6-0, 6-3 victory.

"Of course the first match is always tough, especially here because I didn't play any tournaments for three or four weeks after Wimbledon, but I was feeling pretty good," Li said.

"I was still a little bit nervous, which is natural, but I was fighting a lot on the court and I'm happy to win today."

Bartoli said she was surprised how smoothly she rediscovered her game after her Wimbledon triumph.

"I hadn't played on hard courts for a while, and also the last two times I played in Toronto I lost first round," Bartoli said.

"So I just wanted to enjoy myself on the court and try my hardest, and being able to win 6-0, 6-3 was obviously pretty good for me. I think I played well, and I'm very pleased with the way I handled everything on the court today."

Bartoli had been scheduled to make her post-Wimbledon return in California last week, but had to pull out with a hamstring injury.

"My hamstring is getting better and better," she said.

"I just need to take care of it every day. I was able to work with my physio back home and do some rehabilitation and strength work on it so it gets stronger.

"The summer season is a gruelling season -- you have to be really fit and ready -- so I'm working on it on a daily basis to make sure I'm getting stronger and stronger."

Later on Wednesday, world number one Serena Williams starts her campaign against Italian veteran Francesca Schiavone.